The present invention is directed to an input/output ("I/O") port emulator implemented on a peripheral card for use in connection with a peripheral expansion slot on the Apple II family of computers sold by Apple Computer, Inc. of Cupertino, Calif. More particularly, the invented port emulator, when installed in an Apple II computer, enables the Apple II computer to run software written for personal computers of the type sold by International Business Machines Corporation ("IBM") under the MS-DOS and equivalent operating systems. The present invention utilizes Apple II peripherals such as printers, modems, mouse, and disk drives.
In the following description, references will be made to 8086 microprocessors to represent the family of microprocessors used by IBM personal computers and to 6502 microprocessors for the family of microprocessors used by Apple II personal computers. Various references will be made to the particular architectures of the 8086 and 6502 microprocessors for ease of understanding by those skilled in the relevant art who will be familar with such architectures. Details such as the technique for interfacing peripheral cards with the expansion slots in the Apple II computer will not be set forth herein inasmuch as such details are well known to those skilled in the art.